INDUCIBLE EXPRESSION OF THE ALPHA(1)-ACID GLYCOPROTEIN BY RAT AND HUMAN TYPE-II ALVEOLAR EPITHELIAL-CELLS

alpha(1)-Acid glycoprotein (AGP) is a major acute phase protein in rat and human. AGP has important immunomodulatory functions that are pote ntially important for pulmonary inflammatory response. The liver is th e main tissue for AGP synthesis in the organism, but the expression of AGP in the rat lung has not been investigated. We show that AGP mRNA was induced in the lung of dexamethasone-, turpentine-, or LPS-treated rats, whereas AGP mRNA was not detected in the lung of control rats, In the lung of animals treated intratracheally with LPS, in situ hybri dization showed that AGP gene expression was restricted to cells locat ed in the corners of the alveolus, consistent with an alveolar type II (ATII) cell localization. The inducible expression of the AGP gene wa s confirmed in vitro with SV40 T2 cells and rat ATII cells in primary culture: maximal expression required the presence of dexamethasone, IL -1 and the conditioned medium of alveolar macrophages acted synergisti cally with dexamethasone. Rat ATII cells secreted immunoreactive AGP i n vitro when stimulated with dexamethasone or with a combination of de xamethasone and the conditioned medium of alveolar macrophages. In viv o, in the human lung, we detected immunoreactive AGP in hyperplastic A TII cells, whereas we did not detect AGP in the normal lung, We conclu de that AGP is expressed in the lung in cases of inflammation and that ATII cells are the main source of AGP in the lung.